Photopolymerizable compositions have been used for various purposes. For example, they are used for printing, copying, resist formation and the like, commercially.
In general, these compositions contain ethylenic unsaturated compounds or other types of polymerizable compounds, photopolymerization initiators or photo-polymerization initiator systems and, preferably, solvent-soluble or water or alkali-soluble organic polymer binder compounds. However, the application of many of these known and useful photopolymerizable compositions is restricted because most of the initiators used are activated only by an ultraviolet range of a spectrum.
Further, as a technique for image formation, it is demanded that a visible light ray is used as a light source in place of an ultraviolet ray, or an exposure to light is carried out by scanning with a laser which has a large oscillation strength at a visible light range, for example, an argon ion laser. Accordingly, a photopolymerizable material having high sensitivity to a visible light ray is demanded and, thereby, a photopolymerization initiator having high sensitivity to a visible light ray is required.
As improved photopolymerization initiator systems, there are disclosed a system containing hexaarylbisimidazole in Japanese Patent Kokai No. 292, corresponding to U.S. Pat. No. 4,162,162; a system of an active halogen and 3-keto substituted cumarin compound in Japanese Patent Kokai No. 58-15503, corresponding to U.S. Pat. No. 4,505,793; a system of 3-keto substituted cumarin and N-phenylglycine in Japanese Patent Kokai No. 56-460, corresponding to U.S. Pat. No. 4,278,751 a combination of 3-substituted cumarin and a quinazolinone derivative in Japanese Patent Kokai No. 61-97650 and hexaarylbisimidazole and 3-keto substituted cumarin in Japanese Patent Kokai No. 61-123603.
However, the above photopolymerization initiator systems do not have sufficient sensitivity and, therefore, for exposure to light at a high speed by means of a low power laser it is required to find a more sensitive photopolymerization initiator.